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Speeds and Feeds
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Tooling
High-Speed Steel (HSS)
• First developed in the beginning of the 1900s as an improvement to older high-carbon steel tools.
• T1, the original grade of HSS, superseded by M2.
• Can be hardened up to 65 HRC. Has high toughness, low cost.
• Cobalt grades (HSS-Co), e.g. M35 and M42, have a hardness of 68-70 HRC and improved “hot hardness”, but reduced toughness.
• Rule of thumb is that HSS-Co can be run at 10% higher SFM than normal HSS.
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Powdered Metal (PM)
• Strictly speaking, all cemented carbide is made from powdered metal.
• Similar to carbide, manufactured by sintering powdered HSS with a cobalt binder
• Higher wear resistance and “hot hardness” than HSS-Co, improved toughness over carbide tooling.
• Economical for large diameter end mills compared to solid carbide.
Cemented Carbide• First cemented carbide
developed in post-WWI Germany.
• Cemented carbide is a composite material made by sintering powdered tungsten carbide with cobalt as a binder.
• Can have a hardness up to 92 HRA (≈80HRC).
• Extremely high “hot hardness” and wear resistance, but poor toughness, high cost.
• Stiffness 2-3x higher than steel. Generally 1.5-2x denser than steel.
• Rule of thumb is that carbide can be run at 2x higher SFM than normal HSS.
Hot Hardness
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• Materials normally soften with increasing temperatures.
• Hot hardness corresponds to relationship of a material’s hardness with temperature.
Fig 1: Bayer, Alan M., & Becherer, Bruce A. (1989). High-Speed Tool Steels. ASM Handbook, Volume 16: Machining, pp.51-59
Toughness
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• Can be determined by integrating stress-strain curve. Defined as:𝑒𝑛𝑒𝑟𝑔𝑦
𝑣𝑜𝑙𝑢𝑚𝑒= න
0
𝜀𝑓
𝜎𝛿휀
• Toughness corresponds to the energy a material can absorb before fracture.
Fig 4: Bayer, Alan M., & Becherer, Bruce A. (1989). High-Speed Tool Steels. ASM Handbook, Volume 16: Machining, pp.51-59
Speeds and Feeds
Speed Equation
≈4
Empirically determined(Look this up)
Provided or selected
Calculate this
𝑆𝑝𝑖𝑛𝑑𝑙𝑒 𝑆𝑝𝑒𝑒𝑑 𝑅𝑃𝑀 =12 × 𝐶𝑢𝑡𝑡𝑖𝑛𝑔 𝑆𝑝𝑒𝑒𝑑[𝑆𝐹𝑃𝑀]
π × 𝑇𝑜𝑜𝑙 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟[𝑖𝑛]
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Speeds and Feeds(cont’d.)
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𝑆𝑝𝑖𝑛𝑑𝑙𝑒 𝑆𝑝𝑒𝑒𝑑 𝑅𝑃𝑀 =12 × 𝐶𝑢𝑡𝑡𝑖𝑛𝑔 𝑆𝑝𝑒𝑒𝑑 [𝑆𝐹𝑃𝑀]
π × 𝑇𝑜𝑜𝑙 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟[𝑖𝑛]
Speeds and Feeds(cont’d.)
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𝑆𝑝𝑖𝑛𝑑𝑙𝑒 𝑆𝑝𝑒𝑒𝑑 𝑅𝑃𝑀 =12 × 𝐶𝑢𝑡𝑡𝑖𝑛𝑔 𝑆𝑝𝑒𝑒𝑑 [𝑆𝐹𝑃𝑀]
π × 𝑇𝑜𝑜𝑙 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟[𝑖𝑛]
Speeds and Feeds(cont’d.)
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𝑆𝑝𝑖𝑛𝑑𝑙𝑒 𝑆𝑝𝑒𝑒𝑑 𝑅𝑃𝑀 =12 × 𝐶𝑢𝑡𝑡𝑖𝑛𝑔 𝑆𝑝𝑒𝑒𝑑 [𝑆𝐹𝑃𝑀]
π × 𝑇𝑜𝑜𝑙 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟[𝑖𝑛]
Speeds and Feeds(cont’d.)
Feed Equation
𝐹𝑒𝑒𝑑 𝑅𝑎𝑡𝑒𝑖𝑛
𝑚𝑖𝑛=
𝐶ℎ𝑖𝑝 𝐿𝑜𝑎𝑑𝑖𝑛
𝑡𝑜𝑜𝑡ℎ× # 𝑜𝑓 𝑇𝑒𝑒𝑡ℎ [𝑡𝑜𝑜𝑡ℎ] × 𝑆𝑝𝑖𝑛𝑑𝑙𝑒 𝑆𝑝𝑒𝑒𝑑 [𝑅𝑃𝑀]
Calculate this
Provided or selected Calculated from speed equation
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Empirically determined(Look this up)
Speeds and Feeds(cont’d.)
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𝐹𝑒𝑒𝑑 𝑅𝑎𝑡𝑒𝑖𝑛
𝑚𝑖𝑛=
𝐶ℎ𝑖𝑝 𝐿𝑜𝑎𝑑𝑖𝑛
𝑡𝑜𝑜𝑡ℎ× # 𝑜𝑓 𝑇𝑒𝑒𝑡ℎ [𝑡𝑜𝑜𝑡ℎ] × 𝑆𝑝𝑖𝑛𝑑𝑙𝑒 𝑆𝑝𝑒𝑒𝑑 [𝑅𝑃𝑀]
Speeds and Feeds(cont’d.)
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𝐹𝑒𝑒𝑑 𝑅𝑎𝑡𝑒𝑖𝑛
𝑚𝑖𝑛=
𝐶ℎ𝑖𝑝 𝐿𝑜𝑎𝑑𝑖𝑛
𝑡𝑜𝑜𝑡ℎ× # 𝑜𝑓 𝑇𝑒𝑒𝑡ℎ [𝑡𝑜𝑜𝑡ℎ] × 𝑆𝑝𝑖𝑛𝑑𝑙𝑒 𝑆𝑝𝑒𝑒𝑑 [𝑅𝑃𝑀]
Example
• Suppose you are machining 1018 low carbon steel (mild steel) with a ½” 3F HSS end mill. What spindle speed and feed rate would you use?
• Suppose you are machining grade 5 Titanium with a ¼” 4F carbide end mill. What spindle speed and feed rate would you use?
• Use a calculator.
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Other Considerations
• Tool Coatings
• Coolant/Lubricant
• Chip-breaking (Leaded/Unleaded)
• Work Hardening Rate
• Axial Depth of Cut
• Radial Depth of Cut
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